PROJECT SUMMARY HIV remains one of the most significant public health threats worldwide. Elite controllers are invaluable study subjects because they control HIV in the absence of anti-retroviral therapy. The study of elite controllers has helped elucidate host determinants that promote control of chronic HIV replication. Viral factors that contribute to elite control, however, remain poorly understood. My that Desrosiers, isolates these strains. hypothesize expressed research focuses on individual cases of elite control are associated with highly unusual genetic features in the HIV genome. Since joining the laboratory of Dr. I have accumulated data that form the basis of this application. I have recovered replicating HIV and sequenced full-length viral genomes from three of the eight elite controllers in our cohor t. Two of HIV genomes display highly unusual features that cause a decrease i n he infectivity of laboratory HIV-1 These features are a long V1 domain in Envelope (Env) and a 2 amino acid deletion in Nef. I that highly unusual genetic variations in the HIV-1 genome hinder determinants of infectivity by the virus and/or the host. In Aim #1, will characterize t I the long V1 domain in Env that reduces HIV-1 infectivity. Specifically, I will test whether the reduction in infectivity extends to R5-tropic primary isolates that belong to Group M, subtypes B and C. I will assess whether such a long V1 domain is sufficient to confer resistance to broadly neutralizing antibodies directed against the V1/V2 region of Env. Lastly, I will determine whether a long V1 domain increases the likelihood that HIV-1 isolates become densely O-glycosylated. These questions will be addressed using the well-established TZM-bl cell infectivity and neutralization assays. In Aim #2, I will determine whether the 2 amino acid deletion at positions 54 and 55 of Nef not only reduces HIV-1 infectivity but also interferes with T cell surface marker endocytosis and/or activation of resting T cells to produce IL-2. Specifically, I will introduce the double amino acid deletion into nef of the primary HIV-1 isolate SF2, and will test whether this double deletion impairs endocytosis of MHC-I, CD4 and/or CD3 on human Jurkat T cells. I will clone SF2?54-55 nef into an SIV backbone that has been modified to express only this chimeric nef. I will grow rhesus macaque 221 T cells in the absence of IL-2, and will test whether the induction of IL-2 that follows infection of 221 T cells with SIV is impaired when SIV expresses SF2?54-55 Nef in the absence of endogenous SIV Nef. By studying these highly unusual genetic features in the HIV-1 genomes of our elite controllers, I expect to shed light on the relative importance and functional role of individual HIV genetic elements that may contribute to control of chronic HIV-1 infection. Characterization of the mechanisms by which these genetic variations decrease viral infectivity will likely advance our understanding of viral persistence and viral pathogenesis, including the progression to AIDS.